Project 3

Physiological role of aGPCR autoproteolysis

Project DescriptionAuto-proteolysis is a phenomenon prevalent in Adhesion-GPCRs (aGPCRs). The GPCR proteolysis site (GPS), the location of self-cleavage, is embedded within the extracellular GAIN domain of every aGPCR and located close to the membrane. At an early phase of receptor biosynthesis the GAIN domain catalyzes proteolytic cleavage of an aGPCR pro-receptor into two separate polypeptide chains, NTF and CTF (N- and C-terminal fragments) in the endoplasmic reticulum. Further, the cleavage fragments of an aGPCR re-associate via the broken GAIN domain into a heterodimer and seemingly reconstitute the nascent receptor structure (homogeneric heterodimerisation). This peculiar type of protein maturation is thought to carry biological impact due to its evolutionary conservation. While some evidence suggests that GAIN cleavage is necessary for membrane targeting, other results indicate that NTF/CTF separation and NTF::CTF re-hybridzation are essential steps of the signalling cascade initiated through aGPCRs. Intriguingly, even cross-hybridization of NTF and CTF derived from different aGPCR homologs (heterogeneric heterodimerisation) was proposed to be feasible, and might enable porting of extracellular stimuli to different intracellular signalling routes. However, while previous investigations have established biochemical properties of aGPCR homo- and heterogeneric heterodimerisation, direct evidence of naturally formed aGPCR chimeras remains elusive. This project will address salient questions regarding the occurrence and physiological importance of aGPCR heterodimer formation using in vitro and in vivo models combined with nanoscopical imaging.